In the interests of the environment, and to comply with increasingly stringent regulatory demands, it is necessary to increase the amount of biofuels used in automotive fuels.
Biofuels are combustible fuels, typically derived from biological sources, which result in a reduction in “well-to-wheels” (i.e. from source to combustion) greenhouse gas emissions. In diesel fuels for use in compression ignition engines, the most common biofuels are fatty acid methyl esters (FAMEs) such as rapeseed methyl ester and palm oil methyl ester; these are used in blends with conventional diesel fuel components. However, the oxidative degradation products of FAMEs tend to accumulate in engine oil, causing lubricity issues, which has limited their use to 10% v/v or less in modern FAME/diesel blends. At higher concentrations they can also cause fouling of fuel injectors. FAMEs are also more expensive to produce than other common biofuels such as ethanol, and their world production levels much lower.
Moreover, the addition of a FAME to a diesel fuel formulation can be detrimental to its low temperature performance. FAMEs raise the cloud points and the cold filter plugging points (CFPPs) of diesel fuels with which they are blended, to an extent which increases with increasing FAME concentration in the blend. This can make it difficult to formulate diesel fuel/FAME blends within the relevant regulatory specifications, particularly for colder climates where specifications require maximum cloud points and CFPPs to be lower than in more temperate regions. As a result, there are limits to the concentrations at which FAMEs can be included in diesel fuels, in particular winter grade fuels.
It would be desirable to provide new biofuel-containing diesel fuel formulations which could overcome or at least mitigate this problem.